This invention relates to a water treatment system. More specifically, the invention is for treating water circulating in a device or machine, such as (but not limited to) a cooling tower using ozone, in order to remove from that water bacteria, viruses, yeast, mold, protozoa, algae and/or other biological or chemical components which not only affect the purity and effectiveness of the water in the device, but may also produce corrosion, scaling, oxidation and other effects which damage the hardware, including pipes and machinery containing the water. Removal of these components helps prevent disease, especially Legionella. The invention is also for a cooling tower or other water circulating machine including the water treatment system.
There are various patents in the literature which use cooling tower ozonation systems for inhibiting, reducing or otherwise eliminating biological and other components in aqueous solution systems. For example, U.S. Pat. No. 5,186,841 (Schick) describes a cooling water ozonation system for injecting ozone into a pressurized stream of aqueous solution, allowing the ozone injected stream to flow certain distances at certain velocities so that some of the ozone injected is dissolved. Schick has as an object of the invention the dissolution of increased amount of ozone in an effort to decrease the amount of ozone needed in the system.
U.S. Pat. No. 6,086,772 (Tanimura) describes a method and apparatus for preventing biofouling in cooling water systems by intermittently injecting concentrated ozone into a recirculating line of a cooling water system, in which cooling water is made to circulate in a closed system. U.S. Pat. No. 4,172,786 (Frosch) describes the ozonation of cooling tower water by continuously injecting ozone into water circulating between a cooling tower and heat exchanger so as to inhibit formation of further deposits, promote descaling of existing deposits, and inhibit chemical corrosion.
U.S. Pat. No. 5,106,497 (Finnegan) describes an ozone treatment system utilizing an airlift pump as a mixer and as a circulating means. This patent describes an invention for ozone treatment which eliminates the need for a circulating pump, making substantial energy savings.
Other patents related, but not pertinent, to the present invention of water treatment systems using ozone include: U.S. Pat. No. 4,981,594 (Jones); U.S. Pat. No. 5,879,565 (Kusmierz); U.S. Pat. No. 5,174,901 (Smith); U.S. Pat. No. 3,610,107 (DeLoach); U.S. Pat. No. 4,839,064 (McBurney), and International Applications WO 94/25150 (Rez-Tek) and WO 98/31636 (Enproamerica).
One of the reasons for treating the water in cooling towers (or any other machine circulating water as part of a cooling or purifying mechanism) is that such cooling towers have recently been recognized as a major source of Legionella infection. It is also recognized that ozone is a very effective biocide, small concentrations of which have been shown to have good performance in killing bacteria, yeasts and the like.
Appropriate dosing of ozone in water cooling systems is problematical with many formulae to calculate the amount of ozone needed to treat a given volume of water. Such formulae and calculations often do not take into account the fact that environmental conditions differ from one tower to another, as does the water, temperature and other parameters. Moreover, these parameters may change daily and seasonally at a particular cooling tower. The result has been a trend to use maximum ozone doses possible to ensure that enough ozone will be present to cover all extremes. However, ozone generators are expensive to install and maintain, and since ozone is only marginally soluble in water, excess production outgases into the atmosphere, often creating an offensive ozone smell.
Further, chillers and other hardware will react unfavorably when in contact with ozone. Corrosion is a significant result of high concentrations of ozone within a system. It should, however, also be recognized that while ozone itself may be corrosive, corrosion occurs from too much oxidant, rather than that of a specific type.
Ozone generators required to produce and regulate large amounts of ozone are often quite complex, expensive, require high voltage and current levels and a delicate balancing of power supplies. For these and other reasons, ozone generators are costly and have a poor reputation for dependability. Many existing ozone treatment systems for water simply dissolve as much ozone in the tower water as possible. Generators capable of producing large amounts of ozone are used to develop the maximum possible ozone residual in the tower basin water.
For any biocidal program to be effective, the water must be clean. Therefore, all cooling towers should have a filtration system of some kind, regardless of the biocidal technology used. The finest particles within the system have the greatest relative surface area, and produce the greatest chemical activity. They absorb chemicals used for disinfection or corrosion control, and also consume ozone. As such, and for maximum effectiveness of any water treatment program, particles in the 1-5 micron range, should preferably be removed. Various filter technologies are capable of doing this.
The ozone may be introduced by various methods, including sparging either in the sump itself or in a contacting tower. The contacting tower can also be fed by venturi injection. Another method of introducing ozone is by the aspiration thereof into flowing water with a venturi system. Although this can be effective, it requires a small diameter pipe with limited water volume and specific % pressure differential. When conditions are ideal, the gas and water will only remain mixed for a limited distance, and only then if the pipe is straight and of reasonably small diameter with no bends to increase back pressure.
According to one aspect of the invention, there is provided a water treatment apparatus for treating water in a device using water as a circulating medium, the apparatus comprising: (a) an extractor line for removing water from the device; (b) o z o n e generation means for producing and conveying a supply of ozone; (c) a contactor member having an entry passage for receiving water from the extractor line and ozone from the ozone generation means, and contacting passages for receiving a water and ozone mixture from the entry passage and configured so as to create turbulence to intimately mix the water and ozone along at least a portion of its length, and preferably its entire length; and (d) a return line for receiving and transporting the water and ozone mixture from the contacting passages back to the device.
According to another aspect of the invention, there is provided a water treatment apparatus for treating water in a cooling tower having a water basin, tower fill elements positioned over the water basin and through which water cascades downward for the purposes of cooling the water, the apparatus comprising: (a) a extractor line for removing water from the water basin for cleansing and purification treatment; (b) ozone generation means for producing and conveying a supply of ozone; (c) a contactor member having an entry passage for receiving water from the extractor line and ozone from the ozone generation means, contacting passages for receiving a water and ozone mixture from the entry passage and configured so as to create turbulence to intimately mix the water and ozone along at least a portion of its length, and an exit passage for the water and ozone mixture; and (d) a return line for receiving and transporting the water and ozone mixture from the exit passage, or multiple outlet passages, back to the top of the tower fill, the ozone being removed from the mixture by air stripping when the ozonated water cascades down the tower fill.
According to yet a further aspect of the invention, there is provided a method of treating water to remove bacterial and other impurities therefrom, the method comprising: (a) conveying a supply of water requiring removal of impurities to a receiving passage of a contactor member; (b) injecting a supply of ozone gas into the water in the receiving passage to form a water/ozone mixture; (c) passing the water/ozone mixture through a sealed non-linear passage having a plurality of bends therein to thereby create shear forces producing turbulence to maintain an intimate mixture of the water and ozone; (d) providing the non-linear passage with sufficient length so that the ozone in the water/ozone mixture has sufficient time to destroy at least a portion of the bacterial and other impurities in the water; (e) removing the ozone from the water/ozone mixture; and (f) conveying the purified or partially purified water to a predetermined location for further use.
In one aspect, therefore, the invention removes water to be treated from a sump or basin of a cooling tower system, pumps the water through a series of pipes and passages bent to create shear and turbulence, and introduces controlled amounts of ozone gas into the water as it passes through these passages. The turbulence resulting from the shearing of water flow around bends, preferably 90xc2x0 bends, ensures proper mixing between the water and ozone gas, thus providing an extended opportunity for the ozone to carry out its biocidal activities on the water being so treated. Disinfection occurs in the pipes where the ozone and water are mixed, and the ozone and water are thereafter conveyed in appropriate passages to the top of the cooling tower.
In one aspect, the ozone contacting and mixing with water is accomplished in a contactor device comprised of pipe lengths of predetermined length, preferably about 3 feet long, each of which is connected to horizontal sections, also of predetermined length and preferably approximately 6 inches long. The connection between the vertical pipes and horizontal sections is through an approximately 90xc2x0 elbow. This construction results in a somewhat helical configuration, and facilitates the use of considerable lengths of pipe in a substantially small volume of space.
The vertical and horizontal sections together form a continuous passage through which water is forced, and when the water passes through a 90xc2x0 elbow or bend, the flow of the water is sheared, producing turbulence. This happens at every elbow turn, and at every 90xc2x0 bend. In normal circumstances, the tendency for the water and the ozone gas is to separate, but this is countered at every turn along the length of the passage.
Depending upon the flow rate and the pressure produced by the pump driving the water through the passage, pipes of any suitable diameter and length can be used. A prototype system used approximately 30 feet of 2.5 inch diameter piping, consisting of 5 pipe loops, but systems can be scaled up or tailored so as to be of appropriate size and length for any particular system.
This ozone contacting mechanism for contacting and mixing the ozone gas with the water has benefits not displayed by conventional venturi feeds, inline helical mixers, mixing towers or direct sparging. The contactor described herein causes and maintains intimate contact between the gas and water for an extended mixing length, and sustains this intimate contact more than any other system. It is also fairly inexpensive to build. Importantly, the contactor treats the water in the confined spaces of the piping where bacteria, particles and dissolved chemicals are in contact with the ozone gas phase as well as the dissolved phase. Since ozone is much more concentrated and active in the gaseous phase, the effectiveness of the ozone gas action on the bacteria etc. is increased, thereby allowing relatively low ozone levels to have considerably more effect than much higher concentrations of ozone would have in standard systems that use only the dissolved residual. Therefore, a significant aspect of the present invention is the use of ozone in its active gaseous phase, as opposed to its dissolved phase, for enhanced action against bacteria, other microbiota and dissolved components.
The dissolved and/or gaseous mixture is confined in the pipes comprising the contactor device where the actual disinfection of bacteria, yeasts and other impurities in the water occurs. In contrast to other systems which endeavor to develop high dissolved residuals of ozone in the water, and thereafter convey the ozonated water to the tower to treat the sump, the present system treats the water in the contactor/mixer device, and then returns the water to the sump, already treated and stripped of ozone. Since the water is already disinfected in the contactor device, there is, of course, no need to develop an ozone residual in the sump itself. In fact, the ozone, both residual and gaseous, is removed from the water (as will be described below) before the water reaches the sump, and this ensures that almost any possible corrosion which may be caused when ozonated water passes from the sump to the chiller is prevented. This is accomplished by using the natural tendency of a cooling tower to airstrip water as it passes over the fill elements. Ozonated water from the contactor device is piped into the top of the fill elements, where it is allowed to cascade over the fill from the top of the tower. As it cascades, residual gases, which include ozone, are stripped from the water by the time it reaches the sump. In this way, the benefit of treating the fill elements with ozonated water, and thereby disinfecting them, is achieved. This is in contrast to many other, if not all, existing systems which do not disinfect the fill elements.
Additionally, when the fan of the cooling tower is on, the ozone is outgassed with the aerosol plume, disinfecting it to some degree. Since it is the aerosol plume that spreads Legionella, an important aspect of the invention is therefore the effect of the ozone on the plume itself, causing this disinfection.
Another important aspect of the present invention relates to the treatment of so-called xe2x80x9cprotected areas or surfacesxe2x80x9d within the cooling tower sump. Such protected surfaces and areas may comprise surfaces, corners, recesses, and other nooks and crannies which are by-passed by the water circulating through the sump and cooling tower. The surfaces and recesses generally do not contact water containing disinfectants of any type. These protected areas are more readily able to harbor microbial populations which are therefore not exposed to the biocide, either a chemical biocide or ozonated water, being used to treat the water in the cooling tower, and will therefore form xe2x80x9chot spotsxe2x80x9d of biological activity. In many instances, these protected areas are visible to the naked eye, since they harbor algae or diatoms, forming green or brown coatings on the hardware. Previous systems have attempted to prevent the formation of such biological activity in the protected areas, often unsuccessfully, by developing high residual concentrations of biocide in the sump water in the hopes that sufficient biocide will be present to penetrate to these protected areas, and therefore kill the microbes which are located therein.
In the present invention, the ozone is substantially stripped from the water before it enters the sump once more, and these protected surfaces and recess can be a source of reinfestation of the water. Therefore, in an aspect of the invention, the water treatment system of this invention taps or diverts a flow of ozonated water from the contactor device, before the ozone has been stripped from the water. This tapped flow is diverted through appropriate tubing and passages to outlets, such as nozzles, which can be specifically positioned in the sump, exactly where needed, to direct a small flow of ozonated water to one of these protected areas for spot treatment. In this way, the invention allows for such trouble areas to be treated effectively, but without introducing enough ozone into the sump water to cause corrosion in the sump or chiller loop.
An advantage of the system of the present invention is that it may be less costly to construct and maintain than comparable systems on the market. This is due to the simplicity of its design, and, notably, the fact that there is no need to produce huge quantities of ozone. Since small amounts of ozone are produced, and can be used effectively in the confined space of the contacting device, comparatively little ozone is needed compared to those systems where water in the sump itself is treated with the biocide. As a result, the system may require little in the way of controls, and a single ozone generator would be adequate for most towers. Of course, an appropriate generator can be used, which can be scaled up or down, as the situation requires, for the economical treatment of any size system, as well as the fluctuations in environmental conditions which may require more or less ozone at any particular point in time.